1. Field of the Invention
The present invention relates generally to valves suitable for abrasive fluids, such as drilling mud, under high pressures. More specifically, the invention relates to valve bodies for use in web-seat, stem-guided valves wherein the valve body comprises at least one integral seal retention groove.
2. Background of the Invention
A valve suitable for abrasive fluids such as oil field drilling mud comprises a valve body and a corresponding valve seat, with certain valve bodies incorporating an elastomeric seal within a peripheral seal retention groove. Such a valve is usually mounted in the fluid end of a pump incorporating positive displacement pistons or plungers in multiple cylinders. Such valves are frequently web-seat, stem-guided designs adapted for high pressures and repetitive high-impact loading of the valve body and valve seat. Thus, they are expensive to manufacture, especially the moving portion or valve body. Besides requiring finish machining to close tolerances for adequate sealing, such valve bodies must be made strong enough to resist significant distortion under load with resultant leaks and fatigue failures. Prior efforts to reduce distortion under load by strengthening such valve bodies have generally resulted in higher cost and/or heavier designs which exacerbate sealing problems and/or increase the stress of impact loading on components of the valve assembly.
Commercially important design improvements necessarily reflect the fact that certain mud pump valve body and seat dimensions are effectively limited by industry practices and American Petroleum Institute (API) Standards. For example, the web-seat, stem-guided designs favored for mud pump valves are commonly made compatible with the industry benchmark widely known as the TRW Mission 4-web seat, which determines many valve dimensions. Further, API Standards determine the envelope into which valve bodies and seats must fit to promote interchangeability in the field.
Given these constraints, attempts to reduce fatigue failures and/or improve valve performance have led to xe2x80x9cimprovedxe2x80x9d designs which are more expensive to manufacture and have different failure modes than earlier versions. For example, valve bodies with circular xe2x80x9cChannel-Beamxe2x80x9d sections may incorporate a forged bowl shape as seen, for example, in FIG. 1 of U.S. Pat. No. 5,249,600, the entire patent being incorporated herein by reference. This forged valve body has exceptional stiffness and strength.
But such valve bodies have several disadvantages in manufacture and use. First, rough valve body forgings in the Channel-Beam shape require substantial material removal in finish machining of the integral seal retention groove. Second, an elastomeric seal snapped into the seal retention groove may not fully seat around the entire valve body, causing an out-of-round condition that can result in early valve failure. Third, certain portions of the valve body may be made relatively thin to reduce weight, but such thin portions require particular care during heat treatment to avoid excessive brittleness. Avoidance of thin portions, on the other hand, imposes weight penalties that result in greater impact loading. Similar disadvantages are generally present in other Channel-Beam designs, such as those described in U.S. Pat. Nos. 3,191,617; 3,202,178; 3,742,976; 4,180,097; 5,345,965; and 5,431,186, all incorporated herein by reference.
Notwithstanding their relatively high cost, however, valve bodies having an integral seal retention groove (i.e., a seal retention groove having no removable seal retention plate or other analogous removable structural member) such as the one-piece Channel-Beam design have gained limited industry acceptance. Their high strength and stiffness effectively counter valve body distortion about one or more radial axes (i.e., axes radiating perpendicularly from the valve body""s longitudinal axis of symmetry). This type of distortion is particularly a problem on valve bodies that mate with web seats. Cyclical high pressure applied to such a valve body when it is sealed against a web seat tends to repeatedly force portions of the valve body into the spaces between the seat webs. The periphery of the disc-shaped area of the valve body (commonly called the flange) tends to wrinkle like a cupcake paper, the number of wrinkles being equal to the number of seat webs.
On multi-piece valve bodies (i.e., valve bodies having a removable seal retention plate), such cyclic loading induces fatigue that can lead to further distortion and/or failure of the valve flange. Countering such distortion by simply making the flange thicker increases total valve body weight, which in turn increases wear due to higher impact loading of both the valve body and seat. Valve bodies of Channel-Beam design minimize such distortion in part through their inherent rigidity and strength, but they weigh even more than comparable multi-piece valve bodies and so suffer the disadvantage of higher impact loads in use.
Another important disadvantage of the Channel-Beam design, as noted above, relates to seating of the seal insert. Channel-Beam valve bodies generally incorporate an elastomeric seal insert that snaps into its peripheral seal retention groove. A typical xe2x80x9csnap-onxe2x80x9d seal insert comprises a portion of a toroidal structure such as a plastic or rubber ring that is sized to fit tightly, and thus sealingly, in the peripheral seal retention groove. When properly fitted, the elastomeric seal mates tightly with a corresponding valve seat even though the valve body is slightly distorted and even if small particles carried by the pumped fluid may be trapped between sealing surfaces. Practical advantages of such a seal insert include extended valve life and improved valve performance, but proper fitting and sealing of the elastomeric ring on a valve body is often difficult in the field.
For example, the snap-on insert may not exactly fit the Channel in a Channel-Beam valve body. The installed seal may then be out-of-round, leading to premature seal failure and subsequent failure of the valve body and web seat. When such a seal fails, leaking high-pressure fluid will jet through the initial leak path. If the valve remains in service, the leaking, jetting high-pressure fluid will literally wash away the hardened steel of the valve body and/or seat. Multiple and near-simultaneous failures of a single seal ring may give a valve body flange the appearance of a wrinkled cupcake paper.
Leaks due to seal displacement within a seal retention groove may even occur when elastomeric seals are cast and cured in place unless a special adhesive is first applied to the groove. Such bonding of the cured seal to the groove wall is expensive, and it also tends to reduce the service life of the seal due to internal stress induced as the curing elastomer tends to shrink away from the walls to which it is bound. Additionally, field replacement of such seals is not practical.
Another disadvantage of Channel-Beam valve bodies is their relatively high manufacturing cost. They are expensive to manufacture because the forgings from which they are machined are not near-net-shape. Significant machining time is needed to remove excess material from the seal retention groove (the Channel). Further, because of their characteristic shape, Channel-Beam valve bodies require longer or special nonstandard springs to accommodate the extra depth of the bowl.
Problems associated with high machining and materials costs, as well as seal movement and/or out-of-round seal placement, are reduced in valve bodies which incorporate a separate (removable) seal retention plate which commonly screws or bolts to the valve body to form at least part of one wall of a seal retention groove. Separate seal retention plates can be forged to near-net-shape, and they reduce the time required to correctly replace toroidal sealing rings. But they also raise valve fabrication costs and impose use restrictions. For example, they add excess weight to the moving valve body, aggravating impact loading stress. And a removable seal retention plate must be handled separately from the remainder of the valve body during manufacturing. Additionally, special skills and tools are required for proper assembly of a retention plate and seal ring on a valve body. Finally, the threads often used to secure a retention plate to a valve body are both expensive to machine and, because portions of the threads are relatively thin, they demand special protection during heat treatment. Nevertheless, removable seal retention plates are commonly used because such a plate, as well as the valve body to which it is attached in use, can be forged to a xe2x80x9cnear-net-shapexe2x80x9d which requires relatively little finish machining to achieve a desired final shape.
Unfortunately then, even though forged valve bodies having integral seal retention groves, as in the Channel-Beam design, are inherently stronger than designs requiring a removable seal retention plate, they are generally heavier, more expensive to make, and prone to failure due to seal movement and/or out-of-round seals. What is needed is a valve body having strength and rigidity comparable to that of the Channel-Beam design without the disadvantages of high production costs, seal movement and/or out-of-round seal placement.
Attempts to overcome the cost disadvantage of forged valve bodies having integral seal retention grooves have included elimination of forgings altogether, substituting cast valve bodies instead. Though such castings may be produced to near-net-shape and thereby reduce machining costs, the generally higher cost of the casting process itself, compared to forging, has substantially eliminated any hoped-for reduction in overall cost. Additionally, cast valve bodies generally have lower impact strength compared to similarly shaped forgings. Thus, there is a need for a relatively light weight forged valve body incorporating the strength advantages of an integral seal retention groove and the efficiencies of initially forming to near-net-shape.
The present invention relates to valve bodies for use in web-seat, stem-guided valves wherein the valve body encloses at least one hollow and comprises at least one integral seal retention groove. Such valve bodies are relatively stiff for their weight, resisting distortion about radial axes. Preferred valve bodies of the present invention are made by joining first and second portions through at least one cylindrical web of predetermined minimum thickness. Each of the first and second portions is symmetrical about its own respective longitudinal axis, the two longitudinal axes being colinear when the respective portions are joined to form a valve body. The two colinear axes thus form the valve body""s common longitudinal axis of symmetry, and each cylindrical web is radially spaced apart from and symmetrically disposed about the common longitudinal axis. Such radial spacing is measured as the perpendicular distance between the inner surface of the cylindrical web and the common longitudinal axis.
The first and second valve body portions are preferably formed to near-net-shape before being joined. Joining is preferably by frictional welding (particularly inertia welding), but may be by any means of bonding the corresponding mating surfaces on the first and second portions, including electric arc welding or electron beam welding. Corresponding mating surfaces are substantially circular and have sufficient area to allow adequate strength to be developed across the mating surfaces when the portions are joined. Preferred embodiments of corresponding mating surfaces include a substantially flat or conical washer-shaped circular mating surface on the first portion which may be brought into substantial contact with a circular mating surface of similar size and complementary shape on the second portion to form a circular contact area.
Each of the respective first and second portions preferably comprises a disc-shaped body (called a flange) having first and second opposing sides. A guide stem extends perpendicularly and symmetrically from the first opposing side (that is, along the respective longitudinal axis) and thus away from a circular mating surface that is symmetrically disposed about the respective longitudinal axis on the second opposing disc side.
The mating surface(s) on at least the first valve body portion is(are) preferably on one or more cylindrical bosses arising from the disc-shaped body. When such a first portion is joined through one or more corresponding mating surfaces with a second portion in a valve body of the present invention, the cylindrical boss(es) preferably form most of the cylindrical web(s) that space apart and connect the first and second portions after the respective corresponding mating surfaces are joined (preferably by welding them together). In such an embodiment, only a single weld along each circular contact area of corresponding mating surfaces is needed to join the first and second valve body portions to form a valve body of the present invention.
A space peripherally bounded by the boss on the first valve body portion is incorporated in a hollow enclosed by the valve body (and peripherally bounded by the cylindrical web) as a result of joining the respective first and second portions. Such a hollow may additionally include space comprising, for example, one or more depressions in the first and/or second portions that do not extend peripherally beyond the respective mating surfaces and that are symmetrical about the longitudinal axis.
In alternative embodiments of the valve body of the present invention, both first and second portions may comprise a boss or both may simply have a circular mating surface without a boss. In the latter case, a separate cylindrical web structure of predetermined height may be welded (using two circular welds) between the two portions to establish the desired longitudinal spacing between the respective disc-shaped bodies (that is, the flanges) of the first and second portions.
In valve bodies of the present invention, the desired longitudinal spacing between the respective flanges is determined in part by the dimensions of the integral seal retention groove which is formed peripherally between the first and second portions after they are joined. Seal retention groove dimensions for a valve body intended, for example, be used as a replacement for another valve body previously used with a TRW Mission 4web seat, must match analogous dimensions on the previously used valve body.
Regardless of the methods of fabrication of valve bodies of the present invention, peripheral areas of the respective disc-shaped bodies of the first and second portions substantially form the opposing walls of an integral seal retention groove in the finished valve body. A cylindrical web connecting the two opposing groove walls forms the part of the wall of the seal retention groove that is closest to the valve body""s common longitudinal axis (i.e., the valve body""s axis of symmetry). In such a valve body, relatively little machining is required to achieve a desired final shape because each of the first and second portions is formed to near-net-shape (with certain parts optionally machined to final shape) before the portions are joined. For example, serrations in a seal retention groove wall that would be suitable for retaining a cast-in-place elastomeric valve seal in the seal retention groove may be formed by forging the serrations in the first and/or second portions before they are joined, or by machining the serrations either before or after forging. Forming the serrations by forging may reduce both fabrication and materials costs by reducing or eliminating machining operations. If at least one serration is formed by forging or casting, it may retain its as-forged or as-cast surface, or portions may be machined to produce an as-machined surface before and/or after the portions are joined.
As noted above, in valve bodies of the present invention either or both of the first and second valve body portions may comprise a symmetrical depression (that is, a depression symmetrical about the longitudinal axis of symmetry). The hollow or hollows formed within the valve body when such portions are joined may substantially comprise just the cylindrical space peripherally bounded by a boss comprising a mating surface on one of the valve body portions. The hollow may also be enlarged, and/or its shape may be changed, by incorporating one or two of the symmetrical depressions described above. Any such a hollow will be symmetrical about the common longitudinal axis of the valve body and will be limited peripherally by a cylindrical web.
A hollow thus formed by joining of the first and second portions to make a valve body may be totally enclosed (i.e., not in fluid communication with space outside the valve body). Alternatively, the hollow may be substantially enclosed by the valve body but in fluid communication with space outside the valve body through a fluid passage in the valve body. If present, this fluid passage must be adapted to be sealed so as to prevent fluid entry into the hollow when the valve body is put into service.
The presence or absence of such a fluid passage affects the structure of the finished valve, particularly during carburization. When present, such a passage is preferably formed (as, for example, by drilling) longitudinally in one of the two guide stems. Any such passage is preferably plugged (as, for example, by a welded plug) before the valve body is put into service to prevent drilling mud or other foreign matter from entering the hollow enclosed by the valve body and thus adding weight (perhaps asymmetrically) to the valve body.
The presence of one or more hollows within a valve body of the present invention confers several advantages. Necessary flange stiffness is maintained while the mass of the valve body is reduced, thus reducing impact loading. Adequate valve body stiffness is maintained through the action of one or more cylindrical webs in conjunction with the flanges. Reducing impact loading while maintaining adequate valve body stiffness reduces the incidence of fatigue fractures and extends the service life of elastomeric seals, corresponding valve seats, and the valve bodies themselves.
In a preferred embodiment of a valve body of the present invention, a single interior hollow is substantially symmetrical about the valve body""s common longitudinal axis. The single hollow extends symmetrically along radial axes from the common longitudinal axis peripherally to the cylindrical web, as well as extending along the longitudinal axis to the two disc-shaped bodies (flanges) of the valve body""s respective first and second portions. Should multiple interior hollows be desired, a single cylindrical interior hollow, for example, may be subdivided into a smaller (central) cylindrical hollow plus one or more toroidal spaces symmetrical about the valve body""s common longitudinal axis by the inclusion of one or more additional concentric cylindrical webs. Each web present extends between and thus spaces apart and connects the two disc-shaped bodies that are thus joined in the completed valve body. Inclusion of a center post symmetrical about the longitudinal axis in this example would result in conversion of the smaller cylindrical hollow into an additional (concentric) toroidal shaped hollow enclosed within the valve body.
Each cylindrical web in a valve body of the present invention functions in conjunction with the flanges in a manner analogous to the web of an I-beam. Thus, a cylindrical web imparts resistance to deformation of the valve body about any radial axis. Bending stress about any radial axis, tending to cause wrinkling of the periphery of the valve body, will largely result in corresponding tensile and compressive stresses in adjacent parts of the disc-shaped bodies (that is, flange regions), with relative sparing of the web itself. For this reason, the web thickness can be, and preferably will be, less than the thickness of the respective flange regions where they connect with the web in the finished valve body.
Note that in embodiments of the valve body of the present invention which comprise a plurality of cylindrical webs, the structure resisting bending of the valve body about a radial axis will resemble one or more box beams rather than an I-beam. In such embodiments, two or more concentric cylindrical webs form the box beam webs, and these webs space apart and connect the compression-resisting and tension-resisting members (the flange regions). As described above, distortion about one or more radial axes will result primarily in tension and compression forces in the flange regions with relative sparing of the box beam webs (which can then be made relatively thinner).
Thus, valve bodies of the present invention, whether comprising one or a plurality of interior hollows, are strong and stiff but relatively light-weight compared to competing designs. They are relatively easy to fabricate and require relatively little finish machining. They can reduce overall impact stress concentrations near sealing surfaces of the valve body and valve seat, resulting in improved durability and reduced wear in other components of valve assemblies in which such valve bodies are used.